嘴巴是脸上用来吃饭和说话的部分。我们要保持嘴巴干净，说话要有礼貌。
Zuǐba shì liǎn shang yòng lái chīfàn hé shuōhuà de bùfen. Wǒmen yào bǎochí zuǐba gānjìng, shuōhuà yào yǒu lǐmào.
Mouth is the part of the face used for eating and speaking. We should keep our mouth clean and speak politely.
每天刷牙可以保护嘴巴健康。吃饭时，嘴巴要慢慢嚼，不要说话。
Měitiān shuāyá kěyǐ bǎohù zuǐba jiànkāng. Chīfàn shí, zuǐba yào mànmàn jiáo, bù yào shuōhuà.
Brushing teeth every day protects mouth health. When eating, chew slowly with your mouth and don't talk.
嘴巴 is more common in everyday speech; 嘴 is shorter and often used in compounds.
口 is more formal and used in words like 口水 (saliva) or as a measure word for family members.
嘴唇 specifically refers to the lips, the red part of the mouth.